The present invention relates generally to snow grooming equipment and, more particularly, to a wheel-driven snow grooming vehicle and snow-processing and traction-increasing attachments therefor.
All major ski areas in the United States rely on power-driven snow grooming vehicles for maintaining desirable skiing conditions. One common operation performed by such snow grooming vehicles is mogul leveling. Moguls are small, steep, hard-packed snow mounds which are created, especially on steep terrain, by skiers turning at the same location. During a mogul leveling operation, these steep mounds are bladed down and the snow in the mounds is redistributed to provide a more uniform skiing terrain. A similar operation is performed on narrow ski trails which tend to become "dished out" from ski traffic, i.e. the snow becomes relatively low towards the center of and relatively high towards one or both sides of the trail, especially in areas where the trail turns. As a result, it is necessary for snow grooming vehicles to move snow from the sides of a trail back towards the center. Another operation performed by snow grooming vehicles is packing of newly-fallen snow to create a firm base surface for skiing.
At the present time, nearly all snow grooming vehicles are track-driven or "crawler-type" tractors. One problem with such track-driven tractors is that they are extremely expensive to operate and maintain as compared to wheeled vehicles. For example, a typical track-driven snow grooming vehicle may cost on the order of $40 per hour to maintain and operate, whereas a wheel-driven tractor of comparable power would typically cost on the order of $10 per hour to maintain and operate. Track maintenance is a significant portion of the operating expense for track-driven vehicles. Another problem with track-driven vehicles is that they are generally not suitable for off-season work. The vehicle tracks tend to damage fragile mountain terrain and also damage road and other hard surfaces. In addition, the vehicle tracks themselves are relatively fragile and are easily damaged by operation on surfaces other than snow.
In spite of these drawbacks of track-driven snow grooming vehicles, no wheel-driven tractor has, to date, met with success in snow grooming operations. Wheel-driven tractors that are presently sold for snow grooming operations are adaptations of conventional articulated-frame, agriculture-type tractors which are provided with chain-wrapped flotation tires. It is applicant's belief that there are a number of reasons for the lack of success of such vehicles which have not heretofore been appreciated by the manufacturers or purchasers of such vehicles.
One problem is the inherent instability of an agricultural-type tractor in mountainous terrain. Agricultural tractors usually have a relatively high center of gravity because of an elevated engine placement for avoiding dust, etc. Agricultural tractors generally also have a forwardly-mounted engine placement for balancing out a rear vertical load applied to a tractor rear hitch portion by a pulled agricultural implement such as a plow, etc. In addition, large agricultural tractors are generally provided with articulated frames to facilitate relatively short-radius turns. All of these features, i.e. a high center of gravity, a forwardly-positioned center of gravity, and an articulated frame, create stability problems in steep-terrain operation. An articulated frame causes a lateral momentum shift and wheel base shortening during turning operations which tends to overturn a vehicle, especially when it is moving generally perpendicularly to the slope or "fall line" of a hill in steep-terrain. A high center of gravity of course inherently causes instability, and a forwardly-positioned center of gravity significantly increases instability when the vehicle is traveling in a downhill direction.
Another problem with agricultural tractor designs is that such designs generally do not provide good visibility both forwardly and rearwardly of the vehicle. Such visibility in both the forward and rearward directions is extremely important in snow grooming operations. An operator must constantly adjust to changing terrain and thus must be provided with a clear forward view. The operator must also be able to observe the effect that his snow grooming operations have provided and thus must have a clear rear view.
Another problem associated with agricultural tractor design is that such tractors are intentionally built from extremely massive components for the purpose of providing good traction in flat field-type conditions. The engine power needed for moving this large tractor mass and the mass of towed implements is relatively low in flat-surface type operating conditions. In flat-surface operation, engine power must only overcome the effects of inertia. Since rapid acceleration is not required in tractors' operation, engine power requirements are low. However, in steep-terrain operating conditions, weight substantially increases the tractor engine power requirements, since the tractor engine must, in steep terrain, move the mass of the tractor and the mass of any attached implements against a sizeable component of the force of gravity.
A further drawback of conventional agricultural tractor design is that the standard manual transmissions and standard automatic transmissions provided in such vehicles tend to jerk and cause loss of traction when a gear shift is performed in steep-terrain operating conditions.
Another problem with wheel-driven tractors in snow grooming operations is that flotation wheels provided with chains which are used by such vehicles to increase traction are simply incapable of providing the traction which is generated by the track of a conventional crawler-type snow grooming vehicle. A related problem is that most flotation tire chains require several hours to install. This is a major impediment when the vehicle is to be used for road and parking-lot maintenance as well as slope maintenance because chains generally provide poorer traction in hard surface operating conditions and tend to damage such surfaces.
A problem relating to snow grooming generally is that most snow grooming equipment relies on the traction provided by the snow grooming vehicle for operation. For example, a snow grooming vehicle used to level a mogul field is usually simply provided with a fixed blade mounted on the front of the vehicle. Such a blade is effective when the vehicle is moving downhill, and the driving traction of the vehicle is augmented by the force of gravity. However, in situations when the vehicle is moving in an uphill direction and the force of gravity is acting against the direction of vehicle traction, the traction which is generated by the snow grooming vehicle is often insufficient to accomplish the task at hand. Thus, a vehicle operator is forced to initially drive his vehicle to the top of a slope and then performs most snow grooming operations while the vehicle is moving downhill. A related problem is that in certain extremely steep terrain it is dangerous to operate a snow grooming vehicle in a downhill direction. Thus, in many ski areas, some of the steepest terrain is never groomed at all.